Role of asparagine and asparagine synthetase genes in sunflower ( Helianthus annuus) germination and natural senescence

• Published in: Journal of plant physiology 2006-10, Vol.163 (10), p.1061-1070
• Main Authors: Herrera-Rodríguez, María Begoña, Maldonado, José María, Pérez-Vicente, Rafael
• Format: Article
• Language: English
• Subjects: ammonia; asparagine; Asparagine - biosynthesis; Asparagine - genetics; asparagine synthase (glutamine-hydrolysing); Asparagine synthetase; Aspartate-Ammonia Ligase - genetics; Biological and medical sciences; Cotyledon - chemistry; Cotyledon - genetics; cotyledons; Fundamental and applied biological sciences. Psychology; gene expression regulation; Gene Expression Regulation, Plant; Germination; Helianthus - chemistry; Helianthus - genetics; Helianthus - growth & development; Helianthus annuus; Natural senescence; nitrogen; Nitrogen mobilization; plant biochemistry; plant development; Plant Leaves - chemistry; Plant Leaves - genetics; Plant Leaves - growth & development; plant physiology; Plant physiology and development; seed germination; Senescence and abscission; sucrose; Vegetative apparatus, growth and morphogenesis. Senescence
• ISSN: 0176-1617; 1618-1328
• DOI: 10.1016/j.jplph.2005.10.012

Sunflower ( Helianthus annuus) contains three active asparagine synthetase (EC 6.3.5.4, AS) genes: HAS1, HAS1.1 and HAS2. Asparagine content and AS gene expression were determined during germination and leaf and cotyledon natural senescence to assess the role of asparagine as well as the extent of participation of each AS gene in different nitrogen mobilizing processes. Asparagine accumulated in the dry seed and was the predominant amide throughout germination. During cotyledon senescence, the asparagine level was slightly higher than that of glutamine. The opposite was true for leaf senescence. According to transcript accumulation data, most of the asparagine newly synthesized for germination and cotyledon expansion was due to HAS2 activity, with little contribution of the other AS genes. However, all three genes work together to synthesize asparagine for leaf senescence. The absence of significant AS gene expression in cotyledon senescence differentiates leaf and cotyledon senescence, and suggests a cotyledon-specific regulation.